Seems unlikely to me that Sazed/Marsh would have gotten a bunch of people intentionally killed to move Wax back to the city. It'd be far more in character for them to simply have Marsh show up one day and tell him to, or send a Kandra. Even discounting that, shooting Lessie with an Aluminum bullet would have had a lower body-count and probably been more effective.
That being said, something is definitely up with Tan. Note: in the "gallery" the geologist is posed studying rocks, and someone else is posed flying, therefore presumably is a coinshot. And Tan uses knives, with no mention of them being Aluminum or Obsidian. So even granted that the coinshot was probably just a regular dude with no combat experience who liked easy mode Le Parkour, taking him down with knives without some special advantage doesn't seem in the cards. A Steel Ferring or double twinborn could have done it, but that leads to the question of why he didn't dodge the next shot. It could be he's got an unorthodox mix because of Hemalurgy, but how'd he find the bind points? Given that no one considers the idea that the kidnappings were intended to provide Mistings to spike, and the newspaper Koloss story indicates that no one realizes Koloss are Hemalurgic, it appears Sazed left it out of his book in some manner. Electrum seems unlikely, it shows a cloud of possible futures (it and gold are paired because they're internal, Atium and Malatium are external) but it's like looking at the shadow cloud produced by opposing Atium burners, and presumably it would contain not only Tan getting shot, but also Tan dodging to the left, Tan ducking, Tan dodging to the right, Tan getting shot as a result of any of those, Tan rushing Wax and getting shot, Tan rushing Wax and not getting shot, etc. In theory he could be a Mistborn, but the whole "dying from a single steel bullet" makes that somewhat unlikely even beyond them not being believed to exist at this point in time.
Atium synthling (we need a name for people with Hemalurgically gained powers, and I personally like this one) would be a possibility, I guess. Sazed might not be making new Atium, but burned Atium was inaccessible to Ruin, so the existing Atium power stock is presumably floating around waiting for geodes to solidify into.